1. Field of the Invention
The invention in general relates to fluid detection systems, such as for detecting the presence of fluid pollutants, and in particular a detection system having a large number of probes that can be individually identified and monitored from a central location
2. Description of the Prior Art
U.S. Pat. No. 4,221,125, on an invention of John N. Oliver and Louis M. Sandler and No. 4,116,045 on an invention of Bronson M. Potter are exemplary of systems for detecting the presence of fluid pollutants. Such systems typically involve detection probes that are buried or otherwise placed in the region of possible sources of pollutants, such as gasoline storage tanks. The probes are connected via wires to a central station which monitors the probe status. It is well known in the field that it is important to place a multiplicity of probes about such possible pollution sources so that leakage from any portion of the source and flowing in any direction will be quickly detected.
In one type of prior art fluid detection system, each probe is connected via its own set of wires to a centrally located multiplexer which, in combination with a microprocessor, individually interrogates each of the probes and determines its status, such as whether it is in contract with air, oil, or water. The front panel of the central unit has a set of lights for each probe; e.g. if there are four probes, there will be four sets of lights. The microprocessor actuates the lights associated with each probe to indicate the status of the probe. This system is relatively expensive due to the redundancy of electronic parts and the fact that the probes typically are at large distances (up to 4000 ft) from the central unit and separate connecting wiring is necessary for each probe. In addition, the microprocessor and associated display is relatively expensive. Other systems eliminate the expensive redundancy by utilizing parallel connections to the probes and a single display which is activated if any of the probes detect a pollutant or other sensed condition of interest. However, when a pollutant is detected by such a parallel system, an attendant must then go to each probe and check its status to determine which of the probes detected the condition of interest. Since probes are often long distances apart, this is very time consuming.